2015 2500HD Horn Inop

kevin_nj · December 17, 2019

I've had an intermittent inoperative horn issue for a couple of years now. Horn has been replaced & I cleaned the ground at the frame by the horn. When it fails, it fails from steering wheel switch and key fob, that is one way I know it is not the steering wheel switch/clockspring.

The last time it failed (this past summer), I had an extra pair of hands to help diagnose. We used jumper cables to go from the ground connection at the frame directly to the battery to rule out a bad ground. We discovered we could here the relay clicking in the fuse box located driver side in the engine bay. I wiggled the box and the two large locking connectors nearby and the horn began working again. Periodic testing since that had no failures, until today. Out of ~10 attempts the horn only sounded 3 times. Wiggling the fuse box and nearby connections again did not resolve the failure this time.

I've attempted to remove the fuse box and the connectors to re-seat, but they do not want to release. I'm concerned with breaking something if I force too hard. What is the trick to re-seat these connections?

Is there agreement that I'm on the right track of a bad connection in the area? Since I can hear the relay click, that (to me) rules out the BCM and wiring upstream and leaves me with the connections/wiring leaving the fuse/relay box.

Snowcamo · December 18, 2019

I've had an intermittent inoperative horn issue for a couple of years now. Horn has been replaced & I cleaned the ground at the frame by the horn. When it fails, it fails from steering wheel switch and key fob, that is one way I know it is not the steering wheel switch/clockspring.

The last time it failed (this past summer), I had an extra pair of hands to help diagnose. We used jumper cables to go from the ground connection at the frame directly to the battery to rule out a bad ground. We discovered we could here the relay clicking in the fuse box located driver side in the engine bay. I wiggled the box and the two large locking connectors nearby and the horn began working again. Periodic testing since that had no failures, until today. Out of ~10 attempts the horn only sounded 3 times. Wiggling the fuse box and nearby connections again did not resolve the failure this time.

I've attempted to remove the fuse box and the connectors to re-seat, but they do not want to release. I'm concerned with breaking something if I force too hard. What is the trick to re-seat these connections?

Is there agreement that I'm on the right track of a bad connection in the area? Since I can hear the relay click, that (to me) rules out the BCM and wiring upstream and leaves me with the connections/wiring leaving the fuse/relay box.

A relay clicking doesnt mean itis passing power[emoji106]

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kevin_nj · December 18, 2019

9 minutes ago, Snowcamo said:

A relay clicking doesnt mean itis passing power

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True, but it does mean that the trigger is reaching the relay. I do not see a horn relay in the fuse box. My assumption is that the relay itself is inside of the fuse box. I wonder it that is a serviceable item? Back to Google I go....

Edit to add...

I forgot I'd been down that path before; the horn relay is integrated into the fuse box.

Edited December 18, 2019 by kevin_nj

Snowcamo · December 18, 2019

True, but it does mean that the trigger is reaching the relay. I do not see a horn relay in the fuse box. My assumption is that the relay itself is inside of the fuse box. I wonder it that is a serviceable item? Back to Google I go....

Agreed. Wish i could help with tracing the wiring, but my alldata sub just expired. $20 a year. It pays for it self

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kevin_nj · December 18, 2019

Thanks. I have the basic wiring diagram from the GM Upfitter site. I can not recall if I was getting 12V at the fuse when the horn was inop; will need to check that again when I get a second set of hands again. That would tell be if it is the relay or wiring/circuitry past the fuse.

I think I need to get into the fuse block, I'm just worried about breaking it.

Snowcamo · December 18, 2019

Thanks. I have the basic wiring diagram from the GM Upfitter site. I can not recall if I was getting 12V at the fuse when the horn was inop; will need to check that again when I get a second set of hands again. That would tell be if it is the relay or wiring/circuitry past the fuse.

I think I need to get into the fuse block, I'm just worried about breaking it.

Definitely need a helper. Hope you.get it going.

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Doug_Scott · December 18, 2019

Have you tried touching the relays one at a time while someone else presses the horn pad on the steering wheel? Horns have been working the same way forever. Steering wheel provides the ground for the relay, causing the relay to close, which is supposed to send 12v to the horn. If you can hear the click, you should be able to feel it as well. All those relays in the fuse panels are normally all the same. You could just swap them around. Taking the relay out will wipe the connections off for you as well.

If you are in winter weather like it is here, you may want to get the truck indoors to soften the plastic up making it easier to lift the fuse panel off its base.

kevin_nj · December 18, 2019

I can not locate a physical relay for the horn. My thinking is the relay is on the underside of the mount that holds the fuses.

kevin_nj · January 23, 2020

Turns out the horn itself was faulty again (or the shop didn't actually replace it, it was working the day I took it in and began to fail again within a few weeks). Just an odd coincidence that it worked as long as it did after jiggling the harness and connectors at the fuse/relay box it seems.

For now I've spliced in a cheapo Hella horn set mounted to the spare battery tray bracket. Sounds wimpy as heck, but better than nothing. Have a much more expensive Piaa horn set waiting to go in this weekend, claims to be louder and lower frequency.